“Heat” has always been the issue for the electronic elements in operation, and heat dissipation has become the bottleneck for the development of critical technologies. Currently, with regard to the heat dissipation path of an electronic element, the heat is first transmitted to the surface of the electronic element through internal packaging material, and then is conducted to the external portion of heat source by using a larger heat spreader, wherein fins or fans are added thereon to reinforce the heat convection effect.
Recently, the material for forming heat-dissipation elements is quite a popular topic. With the development of electronic products trending towards lightness and thinness, miniaturization, high performance and high frequency, the heat generation per unit volume is increased accordingly, and thus the heat-dissipation material with higher thermal conductivity is needed. Aluminum extrusion material, such as 6063 aluminum extrusion material, is commonly used as heat-dissipation material for fabricating various heat-dissipation elements. Since the thermal-conductivity of the aluminum extrusion heat-dissipation material is not high, which is merely between 160 W/mK and 180 W/mK, it cannot meet the heat-dissipation requirements of modern electronic elements. Although various modified processes have been developed for the aluminum extrusion heat-dissipation material, such as a bonding fins process, a folding fins process, a modified die casting process, a forging process and a skiving process, etc., yet the bottleneck problem of heat dissipation still cannot be resolved.
Since the high temperature in electrical circuits will affect the operation efficiency of electronic elements, a heat-dissipation module has to be installed for keeping the temperature of the electronic elements below the critical safety temperature, thereby preventing the electronic elements from malfunction and instability caused by overheat. However, the thermal-conductivity of heat-dissipation elements is limited, thus resulting in the bottleneck problem of heat dissipation. Because the thermal-conductivity (about 380 W/mK) of copper is greater than that of aluminum, copper-base heat-dissipation material has been developed nowadays.
For improving the heat conductive efficiency of heat-dissipation elements, the conventional technologies use the addition of diamond powder or carbon powder to promote the heat conduction of composite material. For example, U.S. Pat. No. 6,264,882 disclosed a process for fabricating a composite material having high thermal conductivity and having specific application as a heat sink or heat spreader for high density integrated circuits, and the composite material produced by this process has a thermal conductivity between that of diamond and copper. This process basically consists of sputter coating a metal layer on diamond powder; then compacting them into a porous body; and then infiltrating the porous body with a suitable braze material, thereby producing a dense diamond-copper composite material with a high thermal conductivity. Another conventional technology may first mixing copper powder with carbon powder and a polymer; or mixing copper powder with a carbon-containing polymer uniformly to form a mixture, and then form a copper matrix carbon composite material by removing the polymer in the mixture via multiple high-temperature heat treatments. Still another conventional technology may form a carbon-containing composite material by first coating polyacrylonitrile (PAN) carbon fibers with asphalt, an asphalt derivative or a polymer and then carbonizing and graphitizing.
However, the diamond powder and carbon powder used in the aforementioned conventional technologies are all in particulate form. If only small amount of diamond powder or carbon powder is added in a composite material, the continuity of diamond powder or carbon powder in the composite material is not easy to accomplish, thus having difficulty in improving the heat conduction capability of the composite material. On the other hand, if a large amount of diamond powder or carbon powder is added, then properties of the composite material will be affected. Although PAN carbon fibers may have better continuity, yet the thermal-conductivity of the graphitized PAN carbon fibers is merely between 20 W/mk and 500 W/mk, so that the PAN carbon fibers has limited contribution on promoting the heat conduction capability of the composite material. Further, the conventional technologies often face the poor interfacial problem when the carbon material is compounded with a metal matrix.